Part 10

_Ligaments of the Pelvis._--The ilium and sacrum are articulated at the auricular facet of the ilium and the corresponding rough surface of the sacrum. The joint is an amphiarthrosis, permitting very little movement. A =capsular ligament= surrounds the articular surface, being attached to the bones about its circumference; it is short and strong. Craniad of the capsule is a thick very short ligament, composed of very strong transverse fibres passing from the rough surface of the sacrum to the corresponding rough surface of the ilium. This forms the =lateral iliosacral ligament=, which is united at its caudal border to the capsule.

A strong, wide ligamentous band passes from the dorsal border of the ilium to the sides of the sacrum. This is indistinctly subdivided into several bands, which together represent the =long= and =short posterior iliosacral ligaments= of man.

_Symphysis pelvis._--The medial borders of the pubis and ilium meet in the middle line ventrad of the pelvis and are here united by cartilage. The joint is strengthened by numerous small bands which pass across the line of junction from one side to the other; these occur on both surfaces.

_The Hip-joint._--The hip-joint is an =enarthrosis=, or ball-and-socket joint in which more than half the spherical head of the femur is received into the acetabulum. The depth of the acetabulum is increased by a rim of fibrocartilage about its margin, forming the =labrum glenoidale=. This passes across the acetabular notch, forming the =transverse ligament= of the acetabulum; beneath it blood-vessels and nerves pass into the acetabular cavity.

The =capsule of the joint= is large and loose. It is attached about the margin of the acetabulum, and passes over the head of the femur, to be attached to the bone several millimeters distad of the head. It thus encloses both the head and the neck of the femur.

The =ligamentum teres=, or round ligament, is a very strong, short ligament which passes from the depression in the head of the femur to the bottom of the acetabulum.

=The Knee-joint= (Figs. 60 and 61).--The joint between the femur and the tibia is very complex. The surfaces of the condyles of the femur do not correspond to those of the condyles of the tibia. Between the ends of the two bones are placed two disks of cartilage, the =menisci=, or semilunar cartilages (Fig. 60, _c_ and _d_; Fig. 61, _a_ and _b_), of such a form that the congruity of articular surfaces is restored. Each meniscus has a proximal surface corresponding to the form of one of the condyles of the femur, and a distal surface corresponding to a condyle of the tibia. The menisci are held in position by ligaments. The knee-joint permits not only backward and forward movement, but also a small amount of rotary motion.

The joint has two =capsules=, one on the dorsal (convex) side, the other on the ventral side. The two communicate only by a small passageway lying within the joint between the ends of the bones. The dorsal one is attached to the femur several millimeters proximad of the patellar surface and some distance on each side of the latter. The patella is imbedded in its outer wall, and it is attached to the tibia on the edges of the articular surface of the latter, from the crest to the tuberosities. The capsule is also attached laterally and medially to the sides of the menisci, and is closely united to the patellar ligaments. Its cavity contains a mass of yellow fat.

The ventral capsule is attached to the borders of the articular surfaces of the femur and tibia on their ventral sides, to the menisci, and to the epicondyles of the femur and the tuberosities of the tibia. Its walls are stronger and its cavity smaller than those of the dorsal capsule.

The ligaments of the knee-joint (Figs. 60 and 61), aside from the capsules, may be classified into: (1) those which are connected with the patella; (2) =collateral= ligaments (Fig. 60, _i_ and _j_), which pass from the epicondyles directly distad along the sides of the joint to the tibia or fibula; (3) =crucial= ligaments (Fig. 60, _g_ and _h_; Fig. 61, _c_ and _d_), which cross within the joint from one side of the femur to the opposite side of the tibia; (4) ligaments which hold the menisci in place (Fig. 60, _e_ and _f_; Fig. 61, _e_ and _f_).

(1) LIGAMENTS OF THE PATELLA.--The patella is imbedded in the dorsal wall of the dorsal capsule of the joint. From its distal end a strong tendon or ligament passes distad to the crest of the tibia. This is known as the =ligamentum patellæ=: it may be considered a part of the tendon of M. quadriceps femoris. On the lateral side the capsule of the joint is strengthened by the transverse fibres of the tendon of M. plantaris, which aid in holding the patella in place.

(2) COLLATERAL LIGAMENTS.--Of these there are two. The =ligamentum collaterale fibulare= (Fig. 60, _j_) is attached to the lateral epicondyle of the femur and passes distad across the tendon of the plantaris muscle to the head of the fibula. Dorsad of the fibular ligament and parallel with it passes the tendon of origin of the extensor longus digitorum. The =ligamentum collaterale tibiale= (Fig. 60, _i_; Fig. 61, _g_) begins on the medial epicondyle of the femur and passes distad to the lateral tuberosity of the tibia; part of it passes one to one and a half centimeters distad of the tuberosity to be attached to a rough ridge on the side of the tibia.

(3) CRUCIAL LIGAMENTS.--There are two of these also. The =ligamentum cruciatum anterius=, or anterior crucial ligament (Fig. 60, _g_; Fig. 61, _c_), is a thick, strong ligament which begins on the dorsal part of the proximal end of the tibia nearer the medial side (Fig. 60, _g_), and passes ventrad and proximad, between the ends of the two bones forming the joint, into the intercondyloid fossa of the femur, and becomes attached to the medial surface of the lateral condyle of the femur (Fig. 61, _c_). It is composed of two partially separated bands, forming a slight angle with one another. It is crossed near its dorsal and ventral ends by two of the ligaments of the menisci. The =ligamentum cruciatum posterius=, or posterior crucial ligament (Fig. 60, _h_; Fig. 61, _d_), begins on the tibia at the edge of the popliteal notch (Fig. 61, _d_), nearer the medial side, and passes dorsad and proximad to be attached to the ventral edge of the patellar surface of the femur, in the intercondyloid fossa (Fig. 60, _h_).

(4) LIGAMENTS OF THE MENISCI.--There are five of these, connecting the menisci with the femur or tibia. One (Fig. 60, _e_) passes from the dorsal edge of the medial meniscus (_c_) transversely across the anterior crucial ligament (_g_) to the proximal end of the tibia nearer the lateral side. A second (Fig. 60, _f_) passes from the dorsal margin of the lateral meniscus (_d_) transversely beneath the anterior crucial ligament (_g_) to the proximal end of the tibia nearer the ventral side and medial border. A third (Fig. 61, _f_) passes from the ventral margin of the lateral meniscus obliquely across the anterior crucial ligament (_c_) to the lateral side of the medial condyle of the femur. The fourth (Fig. 61, _e_) is small, passing from the medial angle of the ventral border of the lateral meniscus distad to the popliteal notch. The fifth passes from the ventral border of the medial meniscus laterad beneath the posterior crucial ligament to the proximal end of the tibia, nearer the ventral and lateral sides.

=Articulations between the Tibia and Fibula.=--At the proximal end the fibula is as it were suspended from the distal side of the overhanging lateral tuberosity of the tibia by strong ligamentous tissue. The capsule of the joint is formed by an extension of the capsule of the knee-joint which passes between the tibia and fibula on the ventral side. Forming the dorsolateral wall of this extension is a strong, thick ligament which passes directly from the head of the fibula to the lateral surface of the lateral tuberosity of the tibia. A second more delicate ligament passes from the head of the fibula dorsoproximad to the tubercle laterad of the crest of the tibia, bridging a groove through which passes the tendon of M. extensor longus digitorum.

The tibia and fibula are connected throughout their length by an =interosseus membrane=. This is broad and very thin in its proximal part, narrower and thicker distad.

Distad the two malleoli forming the ends of the fibula and tibia are closely and immovably united. The capsule of the joint is here an extension proximad of the capsule of the articulation with the astragalus. On the dorsal side a short broad band of strong fibres passes from the surface of the tibia obliquely laterodistad to the border of the fibula; this forms the =anterior ligament= of the =lateral malleolus=. On the ventral side a very much weaker set of fibres forms the ventral wall of the articular capsule; it is called the =posterior ligament= of the =lateral malleolus=. Tibia and fibula are also connected on the dorsal side by the =ligamentum transversum cruris=, or transverse ligament of the lower leg (Fig. 91, 5), which spans the tendons of Mm. extensor longus digitorum and tibialis anterior. From the middle of the distal margin of this a slender supporting ligament passes distad and is inserted on the dorsal surface of the tarsus. The grooves in the two malleoli for the passage of the tendons are spanned by ligamentous fibres (retinacula) for holding the tendons in place.

=Articulation between the Leg and the Foot.=--At the distal end there is formed between the two malleoli a deep irregular fossa, into which is received the trochlea of the astragalus. The joint is covered by a large =articular capsule=, which passes also, as above noted, between the tibia and fibula. In addition to the capsule the following ligaments may be distinguished: (_a_) On the lateral side, (1) a short ligament from the fibula to the astragalus, directed toward the proximal end of the foot; (2) a ligament from the fibula to the calcaneus, attached to the latter proximad of the peroneal tubercle; (3) a stronger ligament from the fibula to the calcaneus, lying beneath the last-mentioned and directed toward the proximal end of the bone. (_b_) On the medial side may be distinguished (1) a strong ligament from the tibia (medial malleolus) to the sustentaculum tali, and passing thence onto the scaphoid; (2) a short ligament from the medial malleolus to the astragalus.

=The Tarsus.=--The articulations between the separate bones of the tarsus and between the tarsus and metatarsus have a considerable number of variously communicating articular capsules. The separate bones are connected by many ligaments. The ligaments of the ventral surface (=ligamenta plantaria=) are especially well developed. Here may be noticed particularly a very large =calcaneocuboid= ligament, and a large =calcaneocuneiform= ligament which passes from the sustentaculum tali to the medial cuneiform. Those on the dorsal surface (=ligamenta dorsalia=) are less strong and numerous. Many ligaments, longitudinal, transverse, and oblique, pass also between the separate bones (=ligamenta interossea=). =Ligamenta lateralia=, on the lateral and medial borders of the foot, are also distinguishable. Strauss-Durckheim enumerates ninety-four ligaments of the tarsus; an account of each of these does not form part of the plan of the present work.

The ligaments of the metatarsus and phalanges are of the same general character as in the forelimb. Of these Strauss-Durckheim enumerates thirty-six; they will not be described here.

THE MUSCLES.

=I. THE MUSCLES OF THE SKIN.= (Fig. 62.)

=M. cutaneus maximus= (Fig. 62, _b_).--This is a very large, thin muscle which covers almost the whole side of the body. It arises from the outer surface of the latissimus dorsi (Fig. 68, _m_) near its ventral end and from the bicipital arch (Fig. 65, _t′_) in the axilla; from the linea alba for a considerable distance (two or three inches) caudad of the base of the xiphoid process, and from the thorax over a line joining the axilla and the base of the xiphoid. Sometimes a few fibres take origin from the fascia which covers the pectoantibrachialis on the ventral side of the arm.

From their origin the fibres diverge. The cranial ones curve about the base of the forelimb and are inserted into the skin at or near the middle line caudad of the first thoracic vertebra. The most cranial fibres of all are inserted about one to one and a half centimeters from the middorsal line; thence the line of insertion approaches the middorsal line to reach it at about the eighth or ninth thoracic vertebra. The middle fibres run parallel to the middorsal line in the lumbar and sacral regions as far as the root of the tail, a small bundle passing onto the dorsal side of the tail, another onto the ventral side. The fibres of the caudal portion pass onto the thigh, the ventral ones running in the fold of skin which stretches from thigh to abdomen, and are finally lost in the fascia along a line connecting the knee and the root of the tail. A strong fascia connects the adjacent borders of the cutaneus and platysma and lies over the scapular region.

This muscle lies immediately beneath the integument. It covers the first layer of body muscles.

_Action._--Moves the skin.

=M. platysma= (Figs. 62 and 64, _a_, _a′_, _a″_).--This muscle forms a thin layer of fibres covering the sides of the neck and face, in close relation with the integument. Several more or less distinct portions may be distinguished.

(1) Most of the fibres (_a_) arise from the middorsal line, from the occiput to the first thoracic vertebra, in a narrow fascia common to the muscles of the two sides. The most cranial fibres of this region arise as a small bundle from the external occipital crest, beneath the levator auris longus (Fig. 63, _g_, _g′_).

From this origin in the middle line the fibres pass craniolaterad. The most cranial fibres curve about the ventral side of the ear and pass toward the caudal angle of the eye, where they unite with fibres of the zygomaticus (Fig. 64, _d_) or corrugator supercilii lateralis (Fig. 64, _k_), or pass to the lower eyelid. Caudad of these the fibres cover the side of the face and become lost among the facial muscles, some passing to the lower eyelid, some to the fibrous pad which supports the vibrissæ, some to the angle of the mouth, some to the lower lip. The most ventral fibres meet the fibres of the opposite muscle just ventrad of the symphysis of the mandible.

The ventral free border of the platysma is separated on the ventral side of the neck from the border of the opposite muscle by a wedge-shaped area having its point at the symphysis menti.

The fibres of this portion of the muscle are interrupted by an attachment to the skin, along a line passing from the base of the ear to about the middle of the coracoid border of the scapula, The dorsal (_a_) and ventral (_a′_) portions of the muscle, separated by this line of attachment, are sometimes described as separate muscles (the =supercervicocutaneus= and =cervicofacial=, respectively, of Strauss-Durckheim).

(2) A band of fibres one or two centimeters across (_a″_) arises in the fascia of the side of the neck just craniad of the middle of the coracoid border of the scapula, and passes caudoventrad toward the manubrium, its fibres crossing the fibres of the first part of the platysma at right angles. These fibres become lost in the fascia ventrad of the manubrium, or pass across the middle line to intermingle with the corresponding fibres of the opposite side. This portion of the platysma is sometimes absent.

The platysma is everywhere subcutaneous, except at its dorsocranial angle, where a small bundle of fibres is covered by the levator longus auris. It covers the deeper muscles of the neck and head. Closely attached to its inner surface are the submentalis and depressor conchæ, whose fibres bridge over the ventral interval between the borders of the platysmas of opposite sides.

_Action._--Moves the skin of the face and neck.

=II. THE MUSCLES OF THE HEAD.=

A. SUPERFICIAL MUSCLES.--The most superficial layer of muscles on the face and head is formed by differentiation of the fibres of the platysma. The muscles thus formed are not clearly distinct from each other; in this region sets of fibres differing in direction and in origin or insertion receive separate names even though the different sets of fibres are closely interwoven.

In the quadrangle on the dorsal surface of the head enclosed between the two eyes and the two ears, a thin superficial sheet of fibres is found, in which a number of different sets may be distinguished (Fig. 63). These have received the following names.

=M. intermedius scutulorum= (Fig. 63, _a_).--This consists of a broad thin sheet of transverse fibres between the two external ears. The fibres are attached at either end to the scutiform cartilage (1) of the two ears, and pass without interruption across the middle line. At its cranial edge this muscle is continuous with the corrugator supercilii medialis (_b_); at its lateral edge with the frontoscutularis; at its caudal edge with the levator auris longus (_g_).

_Relations._--Outer surface with the integument. Inner surface with the galea aponeurotica (to which the muscle is closely united), the epicranius muscle (_h_) and the temporal muscle (_n_).

_Action._--Draws the two ears dorsad, toward the middle line.

=M. corrugator supercilii medialis= (_b_).--This consists of a thin sheet of scattered fibres lying craniad of the last and intermingling with it. The fibres take origin near the middle line, pass laterad, then curve craniad, converging, to be inserted into the whole extent of the upper eyelid, especially near the caudal angle. Here the fibres unite with those of the orbicularis oculi (_c_).

This muscle is continuous caudad with the intermedius scutulorum (_a_), craniad with the orbicularis oculi (_c_); laterad with the corrugator supercilii lateralis (_d_). Toward the medial side the fibres lose themselves in a tendinous sheet that joins the galea aponeurotica.

_Relations._--Outer surface with the integument. Inner surface with the frontoscutularis and the skull.

_Action._--Raises the upper eyelid.

=M. orbicularis oculi= (Fig. 63, _c_; Fig. 64, _s_).--This consists of two thin bands of muscle-fibres which lie one in either eyelid parallel to its border and unite at the angle of the eye.

_Origin_ by short tendon-fibres from a tubercle on the surface of the frontal process of the maxillary bone just dorsad of the orbital end of the lachrymal canal and between the two parts of the quadratus labii superioris (Fig. 63, _p_ and _q_).

The muscle splits into two parts which pass into the two eyelids. At the outer angle of the eye the two bands unite by the intervention of tendon-fibres between the muscle-fibre bundles of the two.

_Relations._--Outer surface with the integument. Inner surface with the inner membrane of the eyelid.

_Action._--Closes the eye.

=M. corrugator supercilii lateralis= (Fig. 63, _d_; Fig. 64, _k_).--This consists of a number of scattered fibres which arise from among the fibres of the frontoscutularis, and from the tendon lying just craniad of the external opening of the ear, to which are united also parts of the zygomaticus (Fig. 64, _d_) and submentalis (Fig. 64, _c_). The fibres pass craniad, converging so as to form a narrow band which is inserted at the caudolateral angle of the eye, where it unites with the orbicularis oculi (Fig. 64, _s_). This muscle is continuous on the medial side with the corrugator supercilii medialis (Fig. 64, _j_) and the frontoauricularis, on the lateral side with the platysma.

_Relations._--Outer surface with the integument. Inner surface with the frontal bone and the frontoscutularis.

_Action._--Pulls the angle of the eye caudad; at the same time pulls the external ear craniad.

=M. frontoauricularis.=--A few of the fibres which are attached along the upper eyelid sometimes pass dorsocaudad, mingled with fibres of the corrugatores supercilii medialis and lateralis and the frontoscutularis, to the craniomedial angle of the auricular cartilage, where they unite with the fibres of the adductor auris superior. These fibres are sometimes distinguished as the =frontoauricularis= muscle.

=M. levator auris longus= (Fig. 63, _g_ and _g′_). (Part of the auricularis posterior of man.)--This lies on the caudal half of the dorsal surface of the head, forming a laterocaudal continuation of the intermedius scutulorum (_a_).